Electromagnetic wave measuring apparatus, measuring method, program, and recording medium

ABSTRACT

According to the electromagnetic wave measurement device of the present invention, an electromagnetic wave output device outputs an electromagnetic wave having a frequency equal to or more than 0.01 [THz] and equal to or less than 100 [THz] toward a device under test. An electromagnetic wave detector detects the electromagnetic wave which has transmitted through the device under test. A relative position changing unit changes a relative position of an intersection across which an optical path of the electromagnetic wave transmitting through the device under test and the device under test intersect with respect to the device under test. A characteristic value deriving unit derives a characteristic value of the electromagnetic wave based on a detection result of the electromagnetic wave detector while the characteristic value is associated with an assumed relative position which is the relative position if it is assumed that the electromagnetic wave is not refracted by the device under test. A first association correction unit changes the assumed relative position to an actual relative position, which is the relative position if the refraction of the electromagnetic wave by the device under test is considered, thereby associating the result derived by the characteristic value deriving unit with the actual relative position. A corrected characteristic value deriving unit that derives the characteristic value associated with a predetermined relative position based on an output from the first association correction unit.

BACKGROUND ART

1. Field of the Invention

The present invention relates to tomography using an electromagneticwave (frequency thereof is equal to or more than 0.01 [THz], and equalto or less than 100 [THz]) (such as a terahertz wave (frequency thereofis equal to or more than 0.03 [THz], and equal to or less than 10[THz]), for example).

2. Description of the Prior Art

There has conventionally been the computed tomography (CT) as a methodfor obtaining tomographic information on a device under test. Thismethod conducted while a generator and a detector of the X ray are usedis referred to as X-ray CT. With the X-ray CT, it is possible to acquiretomographic information on a human body in non-destructive andnon-contact manner.

However, it is difficult for the X-ray CT to detect internal states(such as defects and distortions) of industrial products constructed bysemiconductors, plastics, ceramics, woods, and papers (referred to as“raw materials” hereinafter). This is because the X-ray presents a hightransmission property to any materials.

On the other hand, the terahertz wave properly transmits through the rawmaterials of the industrial products described above. Therefore, the CTcarried out while a generator and a detector of the terahertz wave areused (referred to as “terahertz CT” hereinafter) can detect internalstates of the industrial products. Patent Document 1 and Non-PatentDocument 1 describe the terahertz CT.

(Patent Document 1) U.S. Pat. No. 7,119,339(Non-Patent Document 1) S. Wang et al., “Pulsed terahertz tomography,”J. Phys. D, Vol. 37 (2004), R1-R36

SUMMARY OF THE INVENTION

However, according to the terahertz CT, when the terahertz wave isobliquely made incident to or emitted from a device under test (DUT),the terahertz wave is refracted, and thus does not travel straight. Onthis occasion, it is assumed that the refractive index of the ambientair of the DUT is 1, and the refractive index of the DUT for theterahertz CT is more than 1.

Due to the fact that the terahertz wave does not travel straight, theterahertz wave cannot reach a detector, and an image of the DUT cannotthus be obtained at a sufficient sensitivity.

Moreover, due to the fact that the terahertz wave does not travelstraight, a detected terahertz wave may not have traveled straightthrough the DUT before the arrival. Therefore, when an image of the DUTis obtained from the detected terahertz wave, artifacts such asobstructive shadows and pseudo images may appear on the image.

Therefore, it is an object of the present invention, when anelectromagnetic wave (frequency thereof is equal to or more than 0.01[THz] and equal to or less than 100 [THz]) including the terahertz waveis fed to a DUT for measurement, to restrain an adverse effect caused byrefraction of the electromagnetic wave including the terahertz wave bythe DUT.

According to the present invention, an electromagnetic wave measurementdevice includes: an electromagnetic wave output device that outputs anelectromagnetic wave having a frequency equal to or more than 0.01 [THz]and equal to or less than 100 [THz] toward a device under test; anelectromagnetic wave detector that detects the electromagnetic wavewhich has transmitted through the device under test; a relative positionchanging unit that changes a relative position of an intersection acrosswhich an optical path of the electromagnetic wave transmitting throughthe device under test and the device under test intersect with respectto the device under test; a characteristic value deriving unit thatderives a characteristic value of the electromagnetic wave based on adetection result of the electromagnetic wave detector while thecharacteristic value is associated with an assumed relative positionwhich is the relative position if it is assumed that the electromagneticwave is not refracted by the device under test; a first associationcorrection unit that changes the assumed relative position to an actualrelative position, which is the relative position if the refraction ofthe electromagnetic wave by the device under test is considered, therebyassociating the result derived by the characteristic value deriving unitwith the actual relative position; and a corrected characteristic valuederiving unit that derives the characteristic value associated with apredetermined relative position based on an output from the firstassociation correction unit.

According to the thus constructed electromagnetic wave measurementdevice, an electromagnetic wave output device outputs an electromagneticwave having a frequency equal to or more than 0.01 [THz] and equal to orless than 100 [THz] toward a device under test. An electromagnetic wavedetector detects the electromagnetic wave which has transmitted throughthe device under test. A relative position changing unit changes arelative position of an intersection across which an optical path of theelectromagnetic wave transmitting through the device under test and thedevice under test intersect with respect to the device under test. Acharacteristic value deriving unit derives a characteristic value of theelectromagnetic wave based on a detection result of the electromagneticwave detector while the characteristic value is associated with anassumed relative position which is the relative position if it isassumed that the electromagnetic wave is not refracted by the deviceunder test. A first association correction unit changes the assumedrelative position to an actual relative position, which is the relativeposition if the refraction of the electromagnetic wave by the deviceunder test is considered, thereby associating the result derived by thecharacteristic value deriving unit with the actual relative position. Acorrected characteristic value deriving unit that derives thecharacteristic value associated with a predetermined relative positionbased on an output from the first association correction unit.

According to the present invention, an electromagnetic wave measurementdevice includes: an electromagnetic wave output device that outputs anelectromagnetic wave having a frequency equal to or more than 0.01 [THz]and equal to or less than 100 [THz] toward a device under test; anelectromagnetic wave detector that detects the electromagnetic wavewhich has transmitted through the device under test; a relative positionchanging unit that changes a relative position of an intersection acrosswhich an optical path of the electromagnetic wave transmitting throughthe device under test and the device under test intersect with respectto the device under test so that the intersection is at a predeterminedrelative position considering the refraction of the electromagnetic waveby the device under test; and a characteristic value deriving unit thatderives a characteristic value of the electromagnetic wave based on adetection result of the electromagnetic wave detector while thecharacteristic value is associated with the predetermined relativeposition.

According to the thus constructed electromagnetic wave measurementdevice, an electromagnetic wave output device outputs an electromagneticwave having a frequency equal to or more than 0.01 [THz] and equal to orless than 100 [THz] toward a device under test. An electromagnetic wavedetector detects the electromagnetic wave which has transmitted throughthe device under test. A relative position changing unit changes arelative position of an intersection across which an optical path of theelectromagnetic wave transmitting through the device under test and thedevice under test intersect with respect to the device under test sothat the intersection is at a predetermined relative positionconsidering the refraction of the electromagnetic wave by the deviceunder test. A characteristic value deriving unit derives acharacteristic value of the electromagnetic wave based on a detectionresult of the electromagnetic wave detector while the characteristicvalue is associated with the predetermined relative position.

According to the present invention, an electromagnetic wave measurementdevice includes: an electromagnetic wave output device that outputs anelectromagnetic wave having a frequency equal to or more than 0.01 [THz]and equal to or less than 100 [THz] toward a device under test; anelectromagnetic wave detector that detects the electromagnetic wavewhich has transmitted through the device under test; a relative positionchanging unit that changes a relative position of an intersection acrosswhich an optical path of the electromagnetic wave transmitting throughthe device under test and the device under test intersect with respectto the device under test; a characteristic value deriving unit thatderives a characteristic value of the electromagnetic wave based on adetection result of the electromagnetic wave detector while thecharacteristic value is associated with an assumed relative positionwhich is the relative position if it is assumed that the electromagneticwave is not refracted by the device under test; and a second associationcorrection unit that, while the relative position if a refraction of theelectromagnetic wave by the device under test is considered is an actualrelative position, acquires the characteristic value associated with theassumed relative position corresponding to the actual relative positionclosest to a predetermined relative position from the characteristicvalue deriving unit, and associates the acquired characteristic valuewith the predetermined relative position.

According to the thus constructed electromagnetic wave measurementdevice, an electromagnetic wave output device outputs an electromagneticwave having a frequency equal to or more than 0.01 [THz] and equal to orless than 100 [THz] toward a device under test. An electromagnetic wavedetector detects the electromagnetic wave which has transmitted throughthe device under test. A relative position changing unit that changes arelative position of an intersection across which an optical path of theelectromagnetic wave transmitting through the device under test and thedevice under test intersect with respect to the device under test. Acharacteristic value deriving unit derives a characteristic value of theelectromagnetic wave based on a detection result of the electromagneticwave detector while the characteristic value is associated with anassumed relative position which is the relative position if it isassumed that the electromagnetic wave is not refracted by the deviceunder test. A second association correction unit, while the relativeposition if a refraction of the electromagnetic wave by the device undertest is considered is an actual relative position, acquires thecharacteristic value associated with the assumed relative positioncorresponding to the actual relative position closest to a predeterminedrelative position from the characteristic value deriving unit, andassociates the acquired characteristic value with the predeterminedrelative position.

According to the electromagnetic wave measurement device of the presentinvention, the characteristic value may be any one of an attenuationratio, a group delay, and a chromatic dispersion of the electromagneticwave.

According to the electromagnetic wave measurement device of the presentinvention, the relative position may be represented by an angle betweenthe intersection and a predetermined axis, and a coordinate of anorthogonal axis orthogonal to the predetermined axis at an intersectionpoint between the orthogonal axis and the intersection.

The present invention is an electromagnetic wave measurement methodusing an electromagnetic wave measurement device including: anelectromagnetic wave output device that outputs an electromagnetic wavehaving a frequency equal to or more than 0.01 [THz] and equal to or lessthan 100 [THz] toward a device under test; an electromagnetic wavedetector that detects the electromagnetic wave which has transmittedthrough the device under test; and a relative position changing unitthat changes a relative position of an intersection across which anoptical path of the electromagnetic wave transmitting through the deviceunder test and the device under test intersect with respect to thedevice under test; the method including: a characteristic value derivingstep that derives a characteristic value of the electromagnetic wavebased on a detection result of the electromagnetic wave detector whilethe characteristic value is associated with an assumed relative positionwhich is the relative position if it is assumed that the electromagneticwave is not refracted by the device under test; a first associationcorrection step that changes the assumed relative position to an actualrelative position, which is the relative position if the refraction ofthe electromagnetic wave by the device under test is considered, therebyassociating the result derived by the characteristic value deriving stepwith the actual relative position; and a corrected characteristic valuederiving step that derives the characteristic value associated with apredetermined relative position based on a result from the firstassociation correction step.

The present invention is an electromagnetic wave measurement methodusing an electromagnetic wave measurement device including: anelectromagnetic wave output device that outputs an electromagnetic wavehaving a frequency equal to or more than 0.01 [THz] and equal to or lessthan 100 [THz] toward a device under test; an electromagnetic wavedetector that detects the electromagnetic wave which has transmittedthrough the device under test; and a relative position changing unitthat changes a relative position of an intersection across which anoptical path of the electromagnetic wave transmitting through the deviceunder test and the device under test intersect with respect to thedevice under test so that the intersection is at a predeterminedrelative position considering the refraction of the electromagnetic waveby the device under test; the method including: a characteristic valuederiving step that derives a characteristic value of the electromagneticwave based on a detection result of the electromagnetic wave detectorwhile the characteristic value is associated with the predeterminedrelative position.

The present invention is an electromagnetic wave measurement methodusing an electromagnetic wave measurement device including: anelectromagnetic wave output device that outputs an electromagnetic wavehaving a frequency equal to or more than 0.01 [THz] and equal to or lessthan 100 [THz] toward a device under test; an electromagnetic wavedetector that detects the electromagnetic wave which has transmittedthrough the device under test; and a relative position changing unitthat changes a relative position of an intersection across which anoptical path of the electromagnetic wave transmitting through the deviceunder test and the device under test intersect with respect to thedevice under test; the method including: a characteristic value derivingstep that derives a characteristic value of the electromagnetic wavebased on a detection result of the electromagnetic wave detector whilethe characteristic value is associated with an assumed relative positionwhich is the relative position if it is assumed that the electromagneticwave is not refracted by the device under test; and a second associationcorrection step that, while the relative position if a refraction of theelectromagnetic wave by the device under test is considered is an actualrelative position, acquires the characteristic value associated with theassumed relative position corresponding to the actual relative positionclosest to a predetermined relative position from the result derived bythe characteristic value deriving step, and associates the acquiredcharacteristic value with the predetermined relative position.

The present invention is a program of instructions for execution by acomputer to perform an electromagnetic wave measurement process using anelectromagnetic wave measurement device including: an electromagneticwave output device that outputs an electromagnetic wave having afrequency equal to or more than 0.01 [THz] and equal to or less than 100[THz] toward a device under test; an electromagnetic wave detector thatdetects the electromagnetic wave which has transmitted through thedevice under test; and a relative position changing unit that changes arelative position of an intersection across which an optical path of theelectromagnetic wave transmitting through the device under test and thedevice under test intersect with respect to the device under test; theelectromagnetic wave measurement process including: a characteristicvalue deriving step that derives a characteristic value of theelectromagnetic wave based on a detection result of the electromagneticwave detector while the characteristic value is associated with anassumed relative position which is the relative position if it isassumed that the electromagnetic wave is not refracted by the deviceunder test; a first association correction step that changes the assumedrelative position to an actual relative position, which is the relativeposition if the refraction of the electromagnetic wave by the deviceunder test is considered, thereby associating the result derived by thecharacteristic value deriving step with the actual relative position;and a corrected characteristic value deriving step that derives thecharacteristic value associated with a predetermined relative positionbased on a result from the first association correction step.

The present invention is a program of instructions for execution by acomputer to perform an electromagnetic wave measurement process using anelectromagnetic wave measurement device including: an electromagneticwave output device that outputs an electromagnetic wave having afrequency equal to or more than 0.01 [THz] and equal to or less than 100[THz] toward a device under test; an electromagnetic wave detector thatdetects the electromagnetic wave which has transmitted through thedevice under test; and a relative position changing unit that changes arelative position of an intersection across which an optical path of theelectromagnetic wave transmitting through the device under test and thedevice under test intersect with respect to the device under test sothat the intersection is at a predetermined relative positionconsidering the refraction of the electromagnetic wave by the deviceunder test; the electromagnetic wave measurement process including: acharacteristic value deriving step that derives a characteristic valueof the electromagnetic wave based on a detection result of theelectromagnetic wave detector while the characteristic value isassociated with the predetermined relative position.

The present invention is a program of instructions for execution by acomputer to perform an electromagnetic wave measurement process using anelectromagnetic wave measurement device including: an electromagneticwave output device that outputs an electromagnetic wave having afrequency equal to or more than 0.01 [THz] and equal to or less than 100[THz] toward a device under test; an electromagnetic wave detector thatdetects the electromagnetic wave which has transmitted through thedevice under test; and a relative position changing unit that changes arelative position of an intersection across which an optical path of theelectromagnetic wave transmitting through the device under test and thedevice under test intersect with respect to the device under test; theelectromagnetic wave measurement process including: a characteristicvalue deriving step that derives a characteristic value of theelectromagnetic wave based on a detection result of the electromagneticwave detector while the characteristic value is associated with anassumed relative position which is the relative position if it isassumed that the electromagnetic wave is not refracted by the deviceunder test; and a second association correction step that, while therelative position if a refraction of the electromagnetic wave by thedevice under test is considered is an actual relative position, acquiresthe characteristic value associated with the assumed relative positioncorresponding to the actual relative position closest to a predeterminedrelative position from the result derived by the characteristic valuederiving step, and associates the acquired characteristic value with thepredetermined relative position.

The present invention is a computer-readable medium having a program ofinstructions for execution by a computer to perform an electromagneticwave measurement process using an electromagnetic wave measurementdevice including: an electromagnetic wave output device that outputs anelectromagnetic wave having a frequency equal to or more than 0.01 [THz]and equal to or less than 100 [THz] toward a device under test; anelectromagnetic wave detector that detects the electromagnetic wavewhich has transmitted through the device under test; and a relativeposition changing unit that changes a relative position of anintersection across which an optical path of the electromagnetic wavetransmitting through the device under test and the device under testintersect with respect to the device under test; the electromagneticwave measurement process including: a characteristic value deriving stepthat derives a characteristic value of the electromagnetic wave based ona detection result of the electromagnetic wave detector while thecharacteristic value is associated with an assumed relative positionwhich is the relative position if it is assumed that the electromagneticwave is not refracted by the device under test; a first associationcorrection step that changes the assumed relative position to an actualrelative position, which is the relative position if the refraction ofthe electromagnetic wave by the device under test is considered, therebyassociating the result derived by the characteristic value deriving stepwith the actual relative position; and a corrected characteristic valuederiving step that derives the characteristic value associated with apredetermined relative position based on a result from the firstassociation correction step.

The present invention is a computer-readable medium having a program ofinstructions for execution by a computer to perform an electromagneticwave measurement process using an electromagnetic wave measurementdevice including: an electromagnetic wave output device that outputs anelectromagnetic wave having a frequency equal to or more than 0.01 [THz]and equal to or less than 100 [THz] toward a device under test; anelectromagnetic wave detector that detects the electromagnetic wavewhich has transmitted through the device under test; and a relativeposition changing unit that changes a relative position of anintersection across which an optical path of the electromagnetic wavetransmitting through the device under test and the device under testintersect with respect to the device under test so that the intersectionis at a predetermined relative position considering the refraction ofthe electromagnetic wave by the device under test; the electromagneticwave measurement process including: a characteristic value deriving stepthat derives a characteristic value of the electromagnetic wave based ona detection result of the electromagnetic wave detector while thecharacteristic value is associated with the predetermined relativeposition.

The present invention is a computer-readable medium having a program ofinstructions for execution by a computer to perform an electromagneticwave measurement process using an electromagnetic wave measurementdevice including: an electromagnetic wave output device that outputs anelectromagnetic wave having a frequency equal to or more than 0.01 [THz]and equal to or less than 100 [THz] toward a device under test; anelectromagnetic wave detector that detects the electromagnetic wavewhich has transmitted through the device under test; and a relativeposition changing unit that changes a relative position of anintersection across which an optical path of the electromagnetic wavetransmitting through the device under test and the device under testintersect with respect to the device under test; the electromagneticwave measurement process including: a characteristic value deriving stepthat derives a characteristic value of the electromagnetic wave based ona detection result of the electromagnetic wave detector while thecharacteristic value is associated with an assumed relative positionwhich is the relative position if it is assumed that the electromagneticwave is not refracted by the device under test; and a second associationcorrection step that, while the relative position if a refraction of theelectromagnetic wave by the device under test is considered is an actualrelative position, acquires the characteristic value associated with theassumed relative position corresponding to the actual relative positionclosest to a predetermined relative position from the result derived bythe characteristic value deriving step, and associates the acquiredcharacteristic value with the predetermined relative position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of an electromagnetic wavemeasurement device according to a first embodiment of the presentinvention;

FIGS. 2( a) and 2(b) are a plan view of the DUT 1, the electromagneticwave output device 2, the electromagnetic wave detector 4, and the stagefor scanning 6, when the stage for scanning 6 is moved in the Xdirection;

FIGS. 3( a) and 3(b) are plan views of the DUT 1, the electromagneticwave output device 2, the electromagnetic wave detector 4, and the stagefor scanning 6, when the stage for scanning 6 is moved in the θdirection;

FIG. 4 is a functional block diagram showing a configuration of thecross sectional image deriving device 10 according to the firstembodiment;

FIG. 5 is a plane cross sectional view showing an optical path of theelectromagnetic wave passing though the DUT 1 assuming that therefraction does not occur for the sake of a description of theattenuation ratio of the electromagnetic wave.

FIG. 6 shows a measured point (X, θ) for deriving the attenuation ratiog_(m)(X, θ);

FIG. 7 is a plane cross sectional view representing the optical path ofthe electromagnetic wave passing through the DUT 1 for describing theassumed relative position and the actual relative position;

FIG. 8( a) shows assumed measured points and actual measured points whenθ=θ, FIG. 8( b) shows assumed measured points and corresponding actualmeasured points when θ=−2pθ, −pθ, 0, −pθ, and 2pθ, and FIG. 8( c) showsthe attenuation ratio g(x, θ) when θ=0;

FIGS. 9( a) and 9(b) show a method for deriving the attenuation ratiog(X, θ) associated with the assumed measured point;

FIG. 10 describes an operation of the corrected attenuation ratioderiving unit 16 for θ=−2pθ;

FIG. 11 is a diagram showing a configuration of the electromagnetic wavemeasurement device according to the second embodiment of the presentinvention;

FIG. 12 shows an optical path of the electromagnetic wave when the Xintercept of the intersection 100 is X0(=−2pX), and the gradient is 0;

FIG. 13 is a functional block diagram showing a configuration of thecross sectional image deriving device 10 according to the secondembodiment;

FIG. 14 is a functional block diagram showing the configuration of thecross sectional image deriving device 10 according to the thirdembodiment of the present invention; and

FIG. 15 shows assumed measured points and actual measured points fordescribing recorded contents of the corrected measured point recordingunit 15 according to the third embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

A description will now be given of embodiments of the present inventionwith reference to drawings.

First Embodiment

FIG. 1 is a diagram showing a configuration of an electromagnetic wavemeasurement device according to a first embodiment of the presentinvention. The electromagnetic wave measurement device according to thefirst embodiment includes an electromagnetic wave output device 2, anelectromagnetic wave detector 4, a stage for scanning (relative positionchanging unit) 6, a display 8, a cross-sectional image deriving device10, a drive quantity determination unit 22, and a stage drive unit 24.The electromagnetic wave measurement device is used for measuring adevice under test (DUT) 1.

The electromagnetic wave output device 2 outputs an electromagnetic wavehaving a frequency equal to or more than 0.01 [THz] and equal to or lessthan 100 [THz] toward the DUT 1. The frequency of the electromagneticwave output toward the DUT 1 includes a terahertz wave band (such asequal to or more than 0.03 [THz] and equal to or less than 10 [THz]).According to the embodiment of the present invention, it is assumed toemploy a terahertz wave as an example of the electromagnetic wave. Apower of the electromagnetic wave output toward the DUT 1 is I₀.

The terahertz wave output to the DUT 1 transmits through the DUT 1. Theelectromagnetic wave detector 4 detects the electromagnetic wave (suchas a terahertz wave) which has transmitted through the DUT 1.

A point at which the terahertz wave is made incident to the DUT 1 is m,and a point at which the terahertz wave is emitted from the DUT 1 is n.Then, an intersection 100 between an optical path of the electromagneticwave which transmits through the DUT 1 and the DUT 1 is represented as aline mn. Moreover, a planar cross sectional shape of the DUT 1 iscircular, and the center of the circle is a point A.

It should be noted that all points m1, m2, m3, and m4 are points atwhich the terahertz wave is made incident to the DUT 1. All points n1,n2, n3, and n4 are points at which the terahertz wave is emitted fromthe DUT 1.

The stage for scanning (relative position changing unit) 6 changes arelative position of the intersection 100 with respect to the DUT 1. Forexample, the DUT 1 is fixed to the stage for scanning 6, the stage forscanning 6 moves in the X direction and the Z direction (directionperpendicular to the sheet of FIG. 1), and rotates about a line whichpasses through the point A, and is perpendicular to the sheet of FIG. 1(referred to as “movement in the θdirection”).

FIGS. 2( a) and 2(b) are a plan view of the DUT 1, the electromagneticwave output device 2, the electromagnetic wave detector 4, and the stagefor scanning 6, when the stage for scanning 6 is moved in the Xdirection. It should be noted that the DUT 1 contains contents 1 a and 1b.

Referring to FIG. 2( a), when the stage for scanning 6 is moved in the+X direction from the state shown in FIG. 1 (alternatively, theelectromagnetic wave output device 2 and the electromagnetic wavedetector 4 may be moved in the −X direction), the intersection 100 isrepresented by a line m1n1. The relative position of the intersection100 with respect to the DUT 1 is below the point A. The intersection 100passes through the content 1 b.

Referring to FIG. 2( b), when the stage for scanning 6 is moved in the−X direction from the state shown in FIG. 1 (alternatively, theelectromagnetic wave output device 2 and the electromagnetic wavedetector 4 may be moved in the +X direction), the intersection 100 isrepresented by a line m2n2. The relative position of the intersection100 with respect to the DUT 1 is above the point A. The intersection 100passes through the content 1 a.

When the stage for scanning 6 is moved in the X direction, therebychanging the state from that shown in FIG. 2( a) to that shown in FIG.2( b), the relative position of the intersection 100 with respect to theDUT 1 changes from that below the point A to that above the point A.

FIGS. 3( a) and 3(b) are plan views of the DUT 1, the electromagneticwave output device 2, the electromagnetic wave detector 4, and the stagefor scanning 6, when the stage for scanning 6 is moved in the θdirection. It should be noted that the DUT 1 contains the contents 1 aand 1 b.

Referring to FIG. 3( a), when the stage for scanning 6 is moved in the+θ direction from the state shown in FIG. 1 (alternatively, theelectromagnetic wave output device 2 and the electromagnetic wavedetector 4 may be moved in the −θdirection), the intersection 100 isrepresented by a line m3n3. The intersection 100 passes between thecontent 1 a and the content 1 b.

Referring to FIG. 3( b), when the stage for scanning 6 is moved in the−θ direction from the state shown in FIG. 1 (alternatively, theelectromagnetic wave output device 2 and the electromagnetic wavedetector 4 may be moved in the +8 direction), the intersection 100 isrepresented by a line m4n4. The intersection 100 passes through thecontent 1 a.

When the stage for scanning 6 is moved in the θ direction, therebychanging the state from that shown in FIG. 3( a) to that shown in FIG.3( b), the relative position of the intersection 100 with respect to theDUT 1 changes.

As described above, the DUT 1 can be scanned by the stage for scanning6.

The drive quantity determination unit 22 determines how much the stagefor scanning 6 is driven in the X direction and the θ direction. On thisoccasion, it is assumed that a quantity of motion in the X direction ofthe stage for scanning 6 is −X, and a quantity of motion in the θdirection is −θ. Then, the drive quantity determination unit 22 feeds −Xand −θ to the stage drive unit 24. The drive quantity determination unit22 also feeds X and θ to the cross sectional image deriving device 10.

The stage drive unit 24 drives the stage for scanning 6 in the Xdirection and the θ direction by the quantities of motion (−X and −θ)fed by the drive quantity determination unit 22. As a result, theoptical path of the electromagnetic wave traveling from theelectromagnetic wave output device 2 to the DUT 1 is moved from X=0 by Xin the X direction and from θ=0 by θ in the θ direction with respect tothe DUT 1.

The drive quantity determination unit 22 feeds the quantities of motion(X and θ) of the optical path of the electromagnetic wave traveling fromthe electromagnetic wave output device 2 to the DUT 1 to the crosssectional image deriving device 10.

The cross sectional image deriving device 10 derives a cross sectionalimage of a cross section of the DUT 1 made on a plane containing theintersection 100 (the sheet in FIGS. 1, 2(a), 2(b), 3(a), and 3(b)).

The display 8 shows the cross sectional image derived by the crosssectional image deriving device 10. The derived cross sectional image isnumerical data on the two-dimensional cross section of the DUT 1, and atwo-dimensional tomographic cross sectional image of the DUT 1 is shownby associating the numerical data with predetermined colors. It shouldbe noted that a widely known method may be properly employed as themethod for displaying the two-dimensional tomographic cross sectionalimage based on numerical data.

FIG. 4 is a functional block diagram showing a configuration of thecross sectional image deriving device 10 according to the firstembodiment. The cross sectional image deriving device 10 includes an A/Dconverter 11, an attenuation ratio deriving unit (characteristic valuederiving unit) 12, a measured point correction quantity recording unit13, a measured point correction unit (first association correction unit)14, a corrected attenuation ratio deriving unit (correctedcharacteristic value deriving unit) 16, and an inverse radon transformunit 18.

The A/D converter 11 converts a detected result of the electromagneticwave detector 4, which is an analog signal, into a digital signal.

The attenuation ratio deriving unit (characteristic value deriving unit)12 derives a characteristic value of the electromagnetic wave based on adetected result of the electromagnetic wave detector 4. Thecharacteristic value is possibly any one of an attenuation ratio, agroup delay, and a chromatic dispersion of the electromagnetic wave.After acquiring the phase of the electromagnetic wave from the detectedresult of the electromagnetic wave detector 4, the group delay of theelectromagnetic wave can be derived by partially differentiating thephase by the frequency. The chromatic dispersion of the electromagneticwave can be derived by partially differentiating the group delay of theelectromagnetic wave by the frequency.

It should be noted that, in embodiments of the present invention, theattenuation ratio deriving unit (characteristic value deriving unit) 12derives the attenuation ratio g_(m)(X, θ) of the electromagnetic wave.

FIG. 5 is a plane cross sectional view showing an optical path of theelectromagnetic wave passing though the DUT 1 assuming that therefraction does not occur for the sake of a description of theattenuation ratio of the electromagnetic wave.

A power (intensity) of the electromagnetic wave traveling toward the DUT1 is denoted by I₀ and a power of the electromagnetic wave after passingthrough the DUT 1 is denoted by I(X, θ). It should be noted that Xdenotes an X-axis intercept of an intersection 100. In other words, Xdenotes an X-axis coordinate of an intersection point between the X axis(orthogonal axis) and the intersection 100. Moreover, θ denotes an anglebetween the intersection 100 and a horizontal axis (predetermined axis)orthogonal to the X axis. The power of the electromagnetic wave whichhas transmitted through the DUT 1 is associated with (X, θ). Theattenuation ratio of the electromagnetic wave is represented as 1n(I_(o)/I(X, θ)). It should be noted that (X, θ) represents a relativeposition of the intersection 100 with respect to the DUT 1.

The attenuation ratio deriving unit 12 acquires the power I(X, θ) of theelectromagnetic wave which has transmitted through the DUT 1 from theA/D converter 11. X and θ are acquired from the drive quantitydetermination unit 22.

On this occasion, it is assumed that a planar cross section of the DUT 1is a circle having a radius r. Then, the value of X ranges from −r to+r, and the value of θ ranges from −π[rad] to +π[rad]. On this occasion,X and θ are changed within the above respective ranges, thereby derivingthe attenuation ratio g_(m)(X, θ). As the power I₀ of theelectromagnetic wave traveling toward the DUT 1, a known value is fed tothe attenuation ratio deriving unit 12 when the DUT 1 is measured.

FIG. 6 shows a measured point (X, θ) for deriving the attenuation ratiog_(m)(X, θ). FIG. 6 shows (X, θ), which is arguments of the attenuationratio g_(m)(X, θ), on an X 0 coordinate plane in which θ is assigned tothe vertical axis, and X is assigned to the horizontal axis. On thisoccasion, (X, θ) is referred to as measured point. The attenuation ratiog_(m)(X, θ) derived by the attenuation ratio deriving unit 12 isassociated with the measured point (X, θ).

In FIG. 6, for the sake of simple illustration, X (X coordinate of theintersection point between the intersection 100 and the X axis) takesvalues −2pX, −pX, 0, pX, and 2pX, and θ (angle between the intersection100 and the horizontal axis orthogonal to the X axis) takes values −2pθ, −pθ, 0, pθ, and 2pθ. For these combinations of X and θ (5×5=25combinations), the attenuation ratio deriving unit 12 derives theattenuation ratio g_(m)(X, θ). It should be noted that, in order toincrease the accuracy of the attenuation ratio g_(m)(X, θ), the numberof X and θ may be increased.

An attenuation ratio g_(m)(X, θ) corresponding to a black point in FIG.6 represents an attenuation ratio in a rectangular area (pθ in heightand pX in width) in FIG. 6. In other words, it is considered that theattenuation ratio corresponding to the rectangular area (pθ in heightand pX in width) takes the value of the attenuation ratio g_(m)(X, θ)corresponding to the black point at the graphical center of therectangle. For example, it is assumed that an attenuation ratiocorresponding to the inside of a rectangle S (pθ in height and pX inwidth) having a black point Q at the graphic center takes a value of anattenuation ratio g_(m)(−2pX, 0) corresponding to the black point Q.

It should be noted that, the measured point (X, θ), as describedreferring to FIG. 5, represents the relative position (referred to as“assumed relative position”) when it is assumed that the DUT 1 does notrefract the electromagnetic wave. Thus, the attenuation ratio derivingunit 12 derives the attenuation ratio g_(m)(X, θ) while the attenuationratio g_(m)(X, θ) is associated with the assumed relative position(measured point (X, θ)).

The measured point correction quantity recording unit 13 records adifference ΔX of the X coordinate and a difference Δθ of the θcoordinate between the measured point (X, θ) representing the assumedrelative position and a measured point (X′, θ′) representing an actualrelative position which is a relative position considering therefraction of the electromagnetic wave caused by the DUT 1.

FIG. 7 is a plane cross sectional view representing the optical path ofthe electromagnetic wave passing through the DUT 1 for describing theassumed relative position and the actual relative position. It should benoted that a measured point representing the assumed relative positionis denoted by Q(X0, 0) (X0=−2pX, refer to FIG. 6).

First, it is assumed that the electromagnetic wave is made incident tothe DUT 1 orthogonally to the X axis, and the X-axis intercept in atraveling direction thereof is −2pX. Then, if the DUT 1 does not refractthe electromagnetic wave, the assumed relative position (assuming therefraction is not present) of the intersection 100 is represented by ameasured point (−2pX, 0).

However, the electromagnetic wave (such as terahertz wave) passingthrough the DUT 1 is refracted by the DUT 1. On this occasion, it isassumed that the refractive index of the ambient air of the DUT 1 is 1,and the refractive index of the DUT 1 is more than 1. Then, thetraveling direction of the terahertz wave is changed at a point m by therefraction. First, an angle between the traveling direction of theterahertz wave and the horizontal axis changes from 0 [rad] to θ1 [rad].It should be noted that θ1>0. Then, the X-axis intercept X1 of theintersection 100 is represented as X1 >−2pX when the refraction isconsidered. In other words, the actual relative position of theintersection 100 is represented as the measured point (X1, θ1).

In this case, the measured point correction quantity recording unit 13records ΔX=X1−X0=X1+2pX and Δθ=θ1−0=θ1 while ΔX and A θ are associatedwith the assumed relative position (measured point (−2pX, 0)).

The X coordinate X1 of the measured point representing the actualrelative position of the intersection 100 is acquired by adding ΔX tothe X coordinate −2pX of the measured point representing the assumedrelative position. The θ coordinate θ1 of the measured pointrepresenting the actual relative position of the intersection 100 isacquired by adding Δθ to the θ coordinate 0 of the measured pointrepresenting the assumed relative position.

The measured point correction unit (first association correction unit)14 changes the assumed relative position to the actual relativeposition, thereby associating the result derived by the attenuationratio deriving unit 12 with the actual relative position.

The measured point correction unit 14 receives the attenuation ratiog_(m)(X, θ) from the attenuation ratio deriving unit 12. On thisoccasion, the measured point (X, θ) represents the assumed relativeposition of the intersection 100. The measured point correction unit 14reads ΔX and A θ corresponding to the measured point (X, θ) from themeasured point correction quantity recording unit 13. The measured pointcorrection unit 14 adds ΔX to the X coordinate X of the measured point(X, θ), and adds Δθ to the θ coordinate θ of the measured point (X, θ),thereby acquiring the measured point (X+ΔX, θ+Δθ). This measured point(X+ΔX, θ+Δθ) represents the actual relative position of the intersection100. For example, when X=−2pX and θ=0, the actual relative position isrepresented as the measured point (−2pX+ΔX, θ+Δθ)=(X1, θ1) as describedabove.

The measured point correction unit 14 changes the assumed relativeposition (represented by the measured point (X, θ)) of the attenuationratio g_(m)(X, θ) derived by the attenuation ratio deriving unit 12 tothe actual relative position (represented by the measured point (X+ΔX,θ+Δθ)), thereby associating the attenuation ratio g_(m)(X, θ) with theactual relative position (represented by the measured point (X+ΔX,θ+Δθ)). The attenuation ratio g_(m)(X, θ) associated with the actualrelative position is denoted by g(X+ΔX, θ+Δθ). In other words, anassociation g(X+ΔX, θ+Δθ)=g_(m)(X, θ) is set. The measured pointcorrection unit 14 outputs g(X+ΔX, θ+Δθ).

On this occasion, the measured point representing the assumed relativeposition is referred to as assumed measured point, and the measuredpoint representing the actual relative position is referred to as actualmeasured point.

FIG. 8( a) shows assumed measured points and actual measured points whenθ=0, FIG. 8( b) shows assumed measured points and corresponding actualmeasured points when θ=−2pθ, −pθ, 0, pθ, and 2pθ, and FIG. 8( c) showsthe attenuation ratio g(x, 0) when θ=0.

Referring to FIG. 8( a), when the assumed measured point is (0, 0), anouter periphery of the DUT 1 is orthogonal to the optical path of theterahertz wave traveling toward the DUT 1, and, thus, the terahertz wavedoes not refract. Thus, when the assumed measured point is (0, 0), theactual measured point is (0, 0).

When the assumed measured point is (−2pX, 0), the X coordinate of theactual measured point is displaced by ΔX (=X1−X0=X1+2pX) in the Xcoordinate, and the θ coordinate of the actual measured point isdisplaced by Δθ(=θ1−0=θ1), and the actual measured point is (X1, θ1).

When the assumed measured point is (−pX, 0), the X coordinate of theactual measured point is slightly larger than −pX, and the θ coordinateis also slightly larger.

Actual measured points of the assumed measured points (2pX, 0) and (pX,0) are point symmetric with the actual measured points of the assumedmeasured points (−2pX, 0) and (−pX, 0). It should be noted that thecenter of the point symmetry is (0, 0).

On this occasion, since the planar cross section of the DUT 1 is thecircle, ΔX and Δθ are functions of the X coordinate of the assumedmeasured point. On the other hand, even when the θ coordinate of theassumed measured point changes, ΔX and Δθ are constant. Thus, as long asthe X coordinate of the assumed measured point remains constant, ΔX andΔθ are constant.

It should be noted that the embodiment of the present invention can beapplied to a case in which the planar cross section of the DUT 1 is nota circle. The embodiment of the present invention is applicable to acase in which ΔX and Δθ change when the θ coordinate of the assumedmeasured point changes.

In FIG. 8( b), an attenuation ratio associated with an actual measuredpoint represents attenuation ratios in a rectangular area the graphiccenter of which is the actual measured point. In other words, theattenuation ratios corresponding to the rectangular area are representedby the attenuation ratio g(X+ΔX, θ+Δθ) corresponding to the actualmeasured point at the graphic center of the rectangle. For example, anattenuation ratio corresponding to the inside of a rectangle S′ thegraphic center of which is an actual measured point Q′ is represented byan attenuation ratio corresponding to the actual measured point Q′.

It should be noted that the respective rectangles in FIG. 8( b) narrowsas the rectangles approaches the ends in the direction of the X axis.This is because the optical path refracts more (the absolute value of Δ0 increases) as the point approaches the ends on the X axis, and aninterval in terms of the X-axis coordinate between neighboring actualmeasured points decreases. Therefore, the widths of areas represented byattenuation ratios for a certain θ are not even. This implies thatwidths of sampling are uneven.

For example, an attenuation ratio g(X, θ) when θ=0 is an attenuationratio associated with an actual measured point located at the center offigure of a rectangle intersecting a line for θ=0 in FIG. 8( b) by themeasured point correction unit 14. This attenuation ratio is shown inFIG. 8( c). It should be noted that the attenuation ratio can be knownonly in a range equal to or more than −r′ and equal to or less than r′in the X-axis coordinate (0<r′<r). Then, though the attenuation ratio ina range equal to or more than −r and less than −r′ may be set to 0(zero), the attenuation ratio in this range is set to the sameattenuation ratio that is in a range including −r′. Then, though theattenuation ratio in a range more than r′ and equal to or less than rmay be set to 0 (zero), the attenuation ratio in this range is set tothe same attenuation ratio that is in a range including r′.

As is appreciated from the reference to FIG. 8( c), the sampling widthsfor θ=0 (corresponding to a horizontal solid lines in the chart) are noteven.

The corrected attenuation ratio deriving unit (corrected characteristicvalue deriving unit) 16 derives a characteristic value (attenuationratio g(X, θ)) associated with a predetermined relative position (suchas an assumed measured point) based on the output from the measuredpoint correction unit (first association correction unit) 14.

FIGS. 9( a) and 9(b) show a method for deriving the attenuation ratiog(X, θ) associated with the assumed measured point.

FIG. 9( a) is similar to FIG. 8( c). However, intermediate portionsbetween left ends of the respective horizontal lines in the chart ofFIG. 8( c) are linearly interpolated.

The corrected attenuation ratio deriving unit 16 acquires (samples)values at −2pX, −pX, 0, pX, and 2pX in the X coordinate from theattenuation ratio acquired by linearly interpolating the attenuationratio having the uneven sampling widths as shown in FIG. 9( a). Thisresults in even sampling widths pX as shown in FIG. 9( b).

It should be noted that the corrected attenuation ratio deriving unit 16acquires values using the even sampling width pX for θ=−2pθ, −pθ, pθ,and 2pθ in addition to the case of θ=0.

However, it is appreciated that there is no area to which an actualmeasured point corresponds for 0=−2p θ at the left end (X coordinate isclose to −r′) (refer to FIG. 8( b)).

FIG. 10 describes an operation of the corrected attenuation ratioderiving unit 16 for 0=−2p θ. The portion at the left end (the Xcoordinate of which is close to −r′) takes an attenuation ratioassociated with an actual measured point at the center of figure of arectangle A1 separated by one cycle.

When the sampling widths in the θ direction for a certain X are uneven,by the method described referring to FIGS. 9( a) and 9(b), even samplingwidths can be acquired in the θ direction.

The inverse radon transform unit 18 receives the attenuation ratio g(X,θ) associated with the assumed measured point (refer to FIG. 6) from thecorrected attenuation ratio deriving unit 16, and performs the inverseradon transform, thereby acquiring a cross sectional image. The crosssectional image is fed to the display 8. It should be noted that theinverse radon transform unit 18 may determine predetermined colors to beassociated with the cross sectional image, and may provide thedetermined colors to the display 8.

A description will now be given of an operation of the first embodiment.

First, the DUT 1 is fixed to the stage for scanning 6.

The drive quantity determination unit 22 determines how much the stagefor scanning 6 is driven in the X direction and the B direction. Thestage drive unit 24 drives the stage for scanning 6 in the X directionand the θ direction by the quantities of motion (−X and −0) fed by thedrive quantity determination unit 22. As a result, an optical path ofthe electromagnetic wave traveling from the electromagnetic wave outputdevice 2 to the DUT 1 is moved from X=0 by X in the X direction and fromθ=0 by θ in the θ direction with respect to the DUT 1. It should benoted that (X, θ) is the assumed measured point (refer to FIGS. 6 and8).

On this occasion, while the stage for scanning 6 is moved in the Xdirection and the Z direction (direction perpendicular to the sheet ofFIG. 1) as well as in the θ direction, the electromagnetic wave outputdevice 2 outputs the electromagnetic wave having a frequency equal to ormore than 0.01 [THz] and equal to or less than 100 [THz] (such as aterahertz wave) toward the DUT 1. The terahertz wave output to the DUT 1transmits through the DUT 1. The electromagnetic wave which has passedthrough the DUT 1 is detected by the electromagnetic wave detector 4. Inthis way, the DUT 1 is scanned.

The detected result of the electromagnetic wave detector 4 is fed to theA/D converter 11 of the cross sectional image deriving device 10. Thedetected result of the electromagnetic wave detector 4 is converted bythe A/D converter 11 into the digital signal, and the digital signal isfed to the attenuation ratio deriving unit 12.

The attenuation ratio deriving unit 12 derives the attenuation ratiog_(m)(X, θ) associated with the assumed measured point (X, θ) whereX=−2pX, −pX, 0, pX, and 2pX, and θ=−2p θ, −pθ, 0, pθ, and 2pθ (refer toFIGS. 6 and 8).

The measured point correction unit 14 reads ΔX and Δθcorresponding tothe assumed measured point (X, θ) from the measured point correctionquantity recording unit 13, and adds them respectively to X and θ,thereby converting the assumed measured point into an actual measuredpoint. Then, the measured point correction unit 14 associates theattenuation ratio g_(m)(X, θ) with the actual measured point (X+ΔX, θ+Aθ), thereby representing the attenuation ratio g_(m)(X, θ) as g(X+ΔX,θ+Δθ). In other words, an association g(X+ΔX, θ+Δθ)=g_(m)(X, θ) is set.For example, an association g(X1, θ1)=g_(m)(−2pX, 0) is set. Themeasured point correction unit 14 outputs g(X+ΔX, θ+Δθ).

When g(X+ΔX, θ+Δθ) is considered for a certain θ(such as θ=0) (refer toFIG. 8( c)), the sampling widths in the X-axis direction are uneven.This is because the optical path refracts more (the absolute value of Δθincreases) as the point approaches the ends on the X axis, and aninterval in terms of the X-axis coordinate between neighboring actualmeasured points decreases.

Thus, the corrected attenuation ratio deriving unit 16 samples g(X+ΔX,θ+Δθ) acquired from the measured point correction unit 14 at the eveninterval in terms of X axis (as well as θ axis according to necessity)(refer to FIGS. 9( a) and 9(b)). As a result, the corrected attenuationratio deriving unit 16 derives the attenuation ratio g(X, θ) associatedwith the assumed measured point.

The attenuation ratio g(X, θ) output from the corrected attenuationratio deriving unit 16 is transformed by the inverse radon transformunit 18 by means of the inverse radon transform, resulting in the crosssectional image. The cross sectional image is colored, and is thendisplayed by the display 8.

According to the first embodiment, when an electromagnetic wave(frequency thereof is equal to or more than 0.01 [THz] and equal to orless than 100 [THz]) including the terahertz wave is fed to the DUT 1for measurement, it is possible to restrain the adverse effect caused bythe refraction of the electromagnetic wave including the terahertz waveby the DUT 1 since the attenuation ratio is derived considering that theelectromagnetic wave including the terahertz wave is refracted by theDUT 1.

Second Embodiment

FIG. 11 is a diagram showing a configuration of the electromagnetic wavemeasurement device according to the second embodiment of the presentinvention. The electromagnetic wave measurement device according to thesecond embodiment includes the electromagnetic wave output device 2, theelectromagnetic wave detector 4, the stage for scanning (relativeposition changing unit) 6, the display 8, the cross-sectional imagederiving device 10, a corrected drive quantity recording unit 21, thedrive quantity determination unit 22, and the stage drive unit 24. Theelectromagnetic wave measurement device is used for measuring the DUT 1.In the following section, the same components are denoted by the samenumerals as of the first embodiment, and will be explained in no moredetails.

The DUT 1, the electromagnetic wave output device 2, the electromagneticwave detector 4, the stage for scanning (relative position changingunit) 6, and the display 8 are the same as those according to the firstembodiment, and hence description thereof is omitted.

The corrected drive quantity recording unit 21 records ΔX′ and Δθ′.

FIG. 12 shows an optical path of the electromagnetic wave when the Xintercept of the intersection 100 is X0(=−2pX), and the gradient is 0.

When the refraction of the electromagnetic wave (such as a terahertzwave) by the DUT 1 is considered, the angle of the optical path of theelectromagnetic wave traveling toward the DUT 1 with respect to thehorizontal axis is θ2 (<0). Moreover, the X coordinate of the point m atwhich the terahertz wave is made incident to the DUT 1 is −2pX. Then,the X-axis intercept of the optical path of the electromagnetic wavetraveling toward the DUT 1 is X2 (<X0).

Moreover, the assumed measured point (−2pX, 0) represents the relativeposition of the intersection 100 with respect to the DUT 1. In otherwords, in order to locate the relative position of the intersection 100with respect to the DUT 1 to the assumed measured point (−2pX, 0), theX-axis intercept of an extension of the optical path of theelectromagnetic wave traveling from the electromagnetic wave outputdevice 2 to the DUT 1 (referred to as “traveling optical path”) needs tobe X2, and the angle of the traveling optical path with respect to thehorizontal axis needs to be θ2.

On this occasion, ΔX′ is represented as (X-axis intercept of anextension of the actual traveling optical path)−(X coordinate of theassumed measured point), and is recorded in the corrected drive quantityrecording unit 21 while ΔX′ is associated with the coordinate of theassumed measured point. Δθ′ is represented as (angle of the actualtraveling optical path with respect to the horizontal axis)−(θcoordinate of the assumed measured point), and is recorded in thecorrected drive quantity recording unit 21 while t Δθ′ is associatedwith the coordinate of the assumed measured point.

As for the assumed measured point (−2pX, 0), ΔX′=X2−X0=X2+2pX, andΔθ′=θ2−0=θ2. The ΔX′ and Δθ′ are recorded in the corrected drivequantity recording unit 21 while they are associated with the assumedmeasured point (−2pX, 0).

The drive quantity determination unit 22 determines how much the stagefor scanning 6 is driven in the X direction and the θ direction. On thisoccasion, the drive quantity determination unit 22 reads ΔX′ and Δθ′corresponding to the assumed measured point (X, θ) from the correcteddrive quantity recording unit 21.

On this occasion, a quantity of motion in the X direction of the stagefor scanning 6 is −(X+ΔX′), and a quantity of motion in the θ directionis −(θ+Δθ′). The drive quantity determination unit 22 feeds thequantities of motion (−(X+ΔX′) and −(0+Δθ′)) of the stage for scanning 6to the stage drive unit 24. The drive quantity determination unit 22feeds X and θ to the cross sectional image deriving device 10.

The stage drive unit 24 drives the stage for scanning 6 in the Xdirection and the θ direction based on the quantities of motion(−(X+ΔX′) and −(θ+Δθ′)) fed by the drive quantity determination unit 22.As a result, the X-axis intercept of the traveling optical path becomesX+ΔX′ and the angle of the traveling optical path with respect to thehorizontal axis becomes θ+Δθ′.

Consequently, considering the refraction of the electromagnetic wave(such as terahertz wave) by the DUT 1, the stage for scanning (relativeposition changing unit) 6 changes the relative position of theintersection 100 with respect to the DUT 1 so that the intersection 100is at a predetermined relative position (such as the assumed relativeposition).

For example, considering the refraction of the electromagnetic wave(such as terahertz wave) by the DUT 1, the stage for scanning (relativeposition changing unit) 6 causes the relative position of theintersection 100 to locate at the assumed measured point (−2pX, 0). Inother words, the stage for scanning 6 moves so that the X-axis interceptof the traveling optical path is X+ΔX′=−2pX+X2+2pX=X2, and the angle ofthe traveling optical path with respect to the horizontal axis isθ+Δθ′=0+θ2=θ2. Thus, the stage for scanning 6 needs to move by −X2 inthe X direction, and by −θ2 in the θ direction.

FIG. 13 is a functional block diagram showing a configuration of thecross sectional image deriving device 10 according to the secondembodiment. The cross sectional image deriving device 10 includes theA/D converter 11, the attenuation ratio deriving unit (characteristicvalue deriving unit) 12, and the inverse radon transform unit 18.

The AD converter 11 is the same as that of the first embodiment, and adescription thereof, therefore, is omitted.

The attenuation ratio deriving unit (characteristic value deriving unit)12 is the same as that of the first embodiment. It should be noted thatthe attenuation ratio of the electromagnetic wave is associated with (X,θ) acquired from the drive quantity determination unit 22. The point (X,θ) acquired from the drive quantity determination unit 22 is the assumedmeasured point (predetermined relative position). Thus, the attenuationratio deriving unit 12 derives the attenuation ratio of theelectromagnetic wave while the attenuation ratio is associated with thepredetermined relative position (assumed measured point).

The attenuation ratio of the electromagnetic wave is associated with theassumed measured point (refer to FIG. 6), and it is thus appreciatedthat the sampling widths are even both in X and θ directions. Therefore,it is not necessary to provide the corrected attenuation ratio derivingunit 16, which is different from the first embodiment.

The inverse radon transform unit 18 receives the attenuation ratio g(X,θ) associated with the assumed measured point (refer to FIG. 6) from theattenuation ratio deriving unit 12, and performs the inverse radontransform, thereby acquiring a cross sectional image. The crosssectional image is fed to the display 8. It should be noted that theinverse radon transform unit 18 may determine predetermined colors to beassociated with the cross sectional image, and may provide thedetermined colors to the display 8.

A description will now be given of an operation of the secondembodiment.

First, the DUT 1 is fixed to the stage for scanning 6.

The drive quantity determination unit 22 determines how much the stagefor scanning 6 is driven in the X direction and the θ direction. On thisoccasion, the drive quantity determination unit 22 reads ΔX′ and Δθ′corresponding to the assumed measured point (X, θ) from the correcteddrive quantity recording unit 21. Further, the drive quantitydetermination unit 22 sets the quantity of motion in the X direction ofthe stage for scanning 6 to −(X+ΔX′), and the quantity of motion in theθ direction to −(θ+Δθ′).

The stage drive unit 24 drives the stage for scanning 6 in the Xdirection and the θ direction based on the quantities of motion(−(X+αX′) and −(θ+Δθ′)) fed by the drive quantity determination unit 22.As a result, the X-axis intercept of the traveling optical path becomesX+ΔX′ and the angle of the traveling optical path with respect to thehorizontal axis becomes θ+Δθ′.

On this occasion, the relative position of the intersection 100 withrespect to the DUT 1 is represented as the assumed measured point (X,θ). In other words, the X intercept of the intersection 100 is X (Xcoordinate of the assumed measured point), and the angle of theintersection 100 with respect to the horizontal axis is θ(θ coordinateof the assumed measured point).

For example, referring to FIG. 12, the stage for scanning 6 is moved by−X2 in the X direction, and by −θ2 in the θ direction so that the X-axisintercept of the traveling optical path is X2, and the angle of thetraveling optical path with respect to the horizontal axis is θ2. Then,the relative position of the intersection 100 with respect to the DUT 1is represented as the assumed measured point (−2pX, 0).

On this occasion, while the stage for scanning 6 is moved in the Xdirection and the Z direction (direction perpendicular to the sheet ofFIG. 1) as well as in the θ direction, the electromagnetic wave outputdevice 2 outputs the electromagnetic wave having a frequency equal to ormore than 0.01 [THz] and equal to or less than 100[THz] (such as aterahertz wave) toward the DUT 1. The terahertz wave output to the DUT 1transmits through the DUT 1. The electromagnetic wave which has passedthrough the DUT 1 is detected by the electromagnetic wave detector 4. Inthis way, the DUT 1 is scanned.

The detected result of the electromagnetic wave detector 4 is fed to theA/D converter 11 of the cross sectional image deriving device 10. Thedetected result of the electromagnetic wave detector 4 is converted bythe A/D converter 11 into the digital signal, and the digital signal isfed to the attenuation ratio deriving unit 12.

The attenuation ratio deriving unit 12 derives the attenuation ratiog(X, θ) associated with the assumed measured point (X, θ) where X=−2pX,−pX, 0, pX, and 2pX, and θ=−2pθ, 0, −pθ, pθ, and 2p θ(refer to FIG. 6).

The attenuation ratio g(X, θ) output from the attenuation ratio derivingunit 12 is transformed by the inverse radon transform unit 18 by meansof the inverse radon transform, resulting in the cross sectional image.The cross sectional image is colored, and is then displayed by thedisplay 8.

According to the second embodiment, when an electromagnetic wave(frequency thereof is equal to or more than 0.01 [THz] and equal to orless than 100 [THz]) including the terahertz wave is fed to the DUT 1for measurement, considering that the electromagnetic wave (such as theterahertz wave) is refracted by the DUT 1, the stage for scanning 6 isdriven so that the optical path of the electromagnetic wave travelingthrough the DUT 1 is represented by the assumed measured point. As aresult, the adverse effect caused by the refraction by the DUT 1 can berestrained.

Third Embodiment

The configuration of the electromagnetic wave measurement deviceaccording to a third embodiment is similar to that of the firstembodiment (refer to FIG. 1). However, the configuration of the crosssectional image deriving device 10 according to the third embodiment isdifferent from the configuration of the cross sectional image derivingdevice 10 according to the first embodiment.

FIG. 14 is a functional block diagram showing the configuration of thecross sectional image deriving device 10 according to the thirdembodiment of the present invention. The cross sectional image derivingdevice 10 includes the A/D converter 11, the attenuation ratio derivingunit (characteristic value deriving unit) 12, a corrected measured pointrecording unit 15, an attenuation ratio correction unit (secondassociation correction unit) 17, and the inverse radon transform unit18.

The AD converter 11 and the attenuation ratio deriving unit(characteristic value deriving unit) 12 are the same as those of thefirst embodiment, and a description thereof, therefore, is omitted.

The corrected measured point recording unit 15 associates apredetermined relative position (such as an assumed measured point Q1)and an assumed measured point (such as an assumed measured point Q2)corresponding to an actual measured point closest to the predeterminedrelative position (such as an actual measured point R2) with each other,and records the associated points.

As described above, the measured point represents a relative position.Moreover, as described above, the measured point representing theassumed relative position is referred to as assumed measured point, andthe measured point representing the actual relative position is referredto as actual measured point.

Thus, the corrected measured point recording unit 15 associates thepredetermined relative position and the assumed relative positioncorresponding to the actual relative position closest to thepredetermined relative position with each other, and records theassociated positions.

FIG. 15 shows assumed measured points and actual measured points fordescribing recorded contents of the corrected measured point recordingunit 15 according to the third embodiment. It should be noted thatactual measured points corresponding to assumed measured points for θ=0are represented by triangles pointing upward in FIG. 15. Actual measuredpoints corresponding to assumed measured points for θ=pθ are representedby triangles pointing downward.

As described in the first embodiment (refer to FIG. 8( b)), an actualmeasured point corresponding to the assumed measured point Q1(2pX, 0) isR1, and is considerably separated from the assumed measured point Q1. Onthis occasion, an actual measured point corresponding to the assumedmeasured point Q2(2pX, pθ) is R2, and is closer to the assumed measuredpoint Q1 than the actual measured point R1.

The corrected measured point recording unit 15 associates the assumedmeasured point Q1 and the assumed measured point Q2 corresponding to theactual measured point R2 closest to the assumed measured point Q1 witheach other, and records the associated points. The actual measured pointR2 is closer to the assumed measured point Q1 than the actual measuredpoint R1, and, thus, it is appreciated that the attenuation ratio at theassumed measured point Q1 is closer to g_(m)(2pX, pθ) (attenuation ratiocorresponding to the actual measured point R2) than to g_(m)(2pX, 0)(attenuation ratio corresponding to the actual measured point R1).

The attenuation ratio correction unit (second association correctionunit) 17 receives the attenuation ratio g_(m)(X, θ) from the attenuationratio deriving unit 12. On this occasion, the measured point (X, θ)represents the assumed relative position (predetermined relativeposition) of the intersection 100.

On this occasion, the attenuation ratio correction unit 17 reads anassumed measured point corresponding to an actual measured point closestto the assumed measured point (X, θ) from the corrected measured pointrecording unit 15. For example, the attenuation ratio correction unit 17reads the assumed measured point Q2(2pX, pθ) corresponding to the actualmeasured point R2 closest to the assumed measured point Q1(2pX, 0) fromthe corrected measured point recording unit 15.

Further, the attenuation ratio correction unit 17 acquires, from theattenuation ratio deriving unit 12, an attenuation ratio associated withthe assumed measured point read from the corrected measured pointrecording unit 15, and associates the acquired attenuation ratio withthe assumed measured point (X, θ) (predetermined relative position). Forexample, the attenuation ratio correction unit 17 acquires, from theattenuation ratio deriving unit 12, an attenuation ratio g_(m)(2pX, pθ)associated with the assumed measured point Q2(2pX, pθ) read from thecorrected measured point recording unit 15, and associates theattenuation ratio g_(m)(2pX, pθ) with the assumed measured point Q1(2pX,0) (predetermined relative position). In other words, an associationg(2pX, 0)=g_(m)(2pX, pθ) is set.

The attenuation ratio correction unit 17 outputs the attenuation ratiog(X, θ) derived in this way.

The inverse radon transform unit 18 receives the attenuation ratio g(X,θ) associated with the assumed measured point (refer to FIG. 6) from theattenuation ratio correction unit 17, and performs the inverse radontransform, thereby acquiring a cross sectional image. The crosssectional image is fed to the display 8. It should be noted that theinverse radon transform unit 18 may determine predetermined colors to beassociated with the cross sectional image, and may provide thedetermined colors to the display 8.

A description will now be given of an operation of the third embodiment.

An operation until the attenuation ratio deriving unit 12 derives theattenuation ratio g_(m)(X, θ) while the attenuation ratio g_(m)(X, θ) isassociated with the assumed measured point (X, θ) (refer to FIGS. 6 and8) is the same as the operation of the first embodiment.

The attenuation ratio correction unit (second association correctionunit) 17 receives the attenuation ratio g_(m)(X, θ) from the attenuationratio deriving unit 12.

Further, the attenuation ratio correction unit 17 reads the assumedmeasured point corresponding to the measured point (X, θ) from thecorrected measured point recording unit 15. For example, the attenuationratio correction unit 17 reads the assumed measured point Q2(2pX, pθ)corresponding to the actual measured point R2 closest to the assumedmeasured point Q1(2pX, 0) from the corrected measured point recordingunit 15 (refer to FIG. 15).

Further, the attenuation ratio correction unit 17 acquires theattenuation ratio associated with the assumed measured point read fromthe corrected measured point recording unit 15 from the attenuationratio deriving unit 12. The acquired attenuation ratio is associatedwith the assumed measured point (X, θ) (predetermined relativeposition). For example, the attenuation ratio correction unit 17acquires, from the attenuation ratio deriving unit 12, the attenuationratio g_(m)(2pX, pθ) associated with the assumed measured point Q2(2pX,pθ) read from the corrected measured point recording unit 15. Theattenuation ratio g_(m)(2pX, pθ) is associated with the assumed measuredpoint Q1(2pX, 0) (predetermined relative position). In other words, anassociation g(2pX, 0)=g_(m)(2pX, pθ) is set.

The attenuation ratio correction unit 17 outputs the attenuation ratiog(X, θ) derived in this way.

The inverse radon transform unit 18 receives the attenuation ratio g(X,θ) associated with the assumed measured point (refer to FIG. 6) from theattenuation ratio correction unit 17, and performs the inverse radontransform, thereby acquiring a cross sectional image. The crosssectional image is colored, and is then displayed by the display 8.

According to the third embodiment, when an electromagnetic wave(frequency thereof is equal to or more than 0.01 [THz] and equal to orless than 100 [THz]) including the terahertz wave is fed to the DUT 1for measurement, it is possible to restrain the adverse effect caused bythe refraction of the electromagnetic wave including the terahertz waveby the DUT 1 since the attenuation ratio is derived considering that theelectromagnetic wave including the terahertz wave is refracted by theDUT 1.

Moreover, the above-described embodiments may be realized in thefollowing manner. A computer is provided with a CPU, a hard disk, and amedia (such as a floppy disk (registered trade mark) and a CD-ROM)reader, and the media reader is caused to read a medium recording aprogram realizing the above-described respective components such as thecross sectional image deriving device 10, thereby installing the programon the hard disk. This method may also realize the above-describedfunctions.

1. An electromagnetic wave measurement device comprising: anelectromagnetic wave output device that outputs an electromagnetic wavehaving a frequency equal to or more than 0.01 [THz] and equal to or lessthan 100 [THz] toward a device under test; an electromagnetic wavedetector that detects the electromagnetic wave which has transmittedthrough the device under test; a relative position changing unit thatchanges a relative position of an intersection across which an opticalpath of the electromagnetic wave transmitting through the device undertest and the device under test intersect with respect to the deviceunder test; a characteristic value deriving unit that derives acharacteristic value of the electromagnetic wave based on a detectionresult of the electromagnetic wave detector while the characteristicvalue is associated with an assumed relative position which is therelative position if it is assumed that the electromagnetic wave is notrefracted by the device under test; a first association correction unitthat changes the assumed relative position to an actual relativeposition, which is the relative position if the refraction of theelectromagnetic wave by the device under test is considered, therebyassociating the result derived by the characteristic value deriving unitwith the actual relative position; and a corrected characteristic valuederiving unit that derives the characteristic value associated with apredetermined relative position based on an output from the firstassociation correction unit.
 2. An electromagnetic wave measurementdevice comprising: an electromagnetic wave output device that outputs anelectromagnetic wave having a frequency equal to or more than 0.01 [THz]and equal to or less than 100 [THz] toward a device under test; anelectromagnetic wave detector that detects the electromagnetic wavewhich has transmitted through the device under test; a relative positionchanging unit that changes a relative position of an intersection acrosswhich an optical path of the electromagnetic wave transmitting throughthe device under test and the device under test intersect with respectto the device under test so that the intersection is at a predeterminedrelative position considering the refraction of the electromagnetic waveby the device under test; and a characteristic value deriving unit thatderives a characteristic value of the electromagnetic wave based on adetection result of the electromagnetic wave detector while thecharacteristic value is associated with the predetermined relativeposition.
 3. An electromagnetic wave measurement device comprising: anelectromagnetic wave output device that outputs an electromagnetic wavehaving a frequency equal to or more than 0.01 [THz] and equal to or lessthan 100 [THz] toward a device under test; an electromagnetic wavedetector that detects the electromagnetic wave which has transmittedthrough the device under test; a relative position changing unit thatchanges a relative position of an intersection across which an opticalpath of the electromagnetic wave transmitting through the device undertest and the device under test intersect with respect to the deviceunder test; a characteristic value deriving unit that derives acharacteristic value of the electromagnetic wave based on a detectionresult of the electromagnetic wave detector while the characteristicvalue is associated with an assumed relative position which is therelative position if it is assumed that the electromagnetic wave is notrefracted by the device under test; and a second association correctionunit that, while the relative position if a refraction of theelectromagnetic wave by the device under test is considered is an actualrelative position, acquires the characteristic value associated with theassumed relative position corresponding to the actual relative positionclosest to a predetermined relative position from the characteristicvalue deriving unit, and associates the acquired characteristic valuewith the predetermined relative position.
 4. The electromagnetic wavemeasurement device according to claim 1, wherein the characteristicvalue is any one of an attenuation ratio, a group delay, and a chromaticdispersion of the electromagnetic wave.
 5. The electromagnetic wavemeasurement device according to claim 1, wherein the relative positionis represented by an angle between the intersection and a predeterminedaxis, and a coordinate of an orthogonal axis orthogonal to thepredetermined axis at an intersection point between the orthogonal axisand the intersection.
 6. An electromagnetic wave measurement methodusing an electromagnetic wave measurement device including: anelectromagnetic wave output device that outputs an electromagnetic wavehaving a frequency equal to or more than 0.01 [THz] and equal to or lessthan 100 [THz] toward a device under test; an electromagnetic wavedetector that detects the electromagnetic wave which has transmittedthrough the device under test; and a relative position changing unitthat changes a relative position of an intersection across which anoptical path of the electromagnetic wave transmitting through the deviceunder test and the device under test intersect with respect to thedevice under test; said method comprising: deriving a characteristicvalue of the electromagnetic wave based on a detection result of theelectromagnetic wave detector while the characteristic value isassociated with an assumed relative position which is the relativeposition if it is assumed that the electromagnetic wave is not refractedby the device under test; changing the assumed relative position to anactual relative position, which is the relative position if therefraction of the electromagnetic wave by the device under test isconsidered, thereby associating the result derived by the deriving ofthe characteristic value with the actual relative position; and derivingthe characteristic value associated with a predetermined relativeposition based on a result from the changing of the assumed relativeposition to an actual relative position.
 7. An electromagnetic wavemeasurement method using an electromagnetic wave measurement deviceincluding: an electromagnetic wave output device that outputs anelectromagnetic wave having a frequency equal to or more than 0.01 [THz]and equal to or less than 100 [THz] toward a device under test; anelectromagnetic wave detector that detects the electromagnetic wavewhich has transmitted through the device under test; and a relativeposition changing unit that changes a relative position of anintersection across which an optical path of the electromagnetic wavetransmitting through the device under test and the device under testintersect with respect to the device under test so that the intersectionis at a predetermined relative position considering the refraction ofthe electromagnetic wave by the device under test; said methodcomprising: deriving a characteristic value of the electromagnetic wavebased on a detection result of the electromagnetic wave detector whilethe characteristic value is associated with the predetermined relativeposition.
 8. An electromagnetic wave measurement method using anelectromagnetic wave measurement device including: an electromagneticwave output device that outputs an electromagnetic wave having afrequency equal to or more than 0.01 [THz] and equal to or less than 100[THz] toward a device under test; an electromagnetic wave detector thatdetects the electromagnetic wave which has transmitted through thedevice under test; and a relative position changing unit that changes arelative position of an intersection across which an optical path of theelectromagnetic wave transmitting through the device under test and thedevice under test intersect with respect to the device under test; saidmethod comprising: deriving a characteristic value of theelectromagnetic wave based on a detection result of the electromagneticwave detector while the characteristic value is associated with anassumed relative position which is the relative position if it isassumed that the electromagnetic wave is not refracted by the deviceunder test; and while the relative position if a refraction of theelectromagnetic wave by the device under test is considered is an actualrelative position, acquiring the characteristic value associated withthe assumed relative position corresponding to the actual relativeposition closest to a predetermined relative position from the result ofderiving a characteristic value of the electromagnetic wave, andassociating the acquired characteristic value with the predeterminedrelative position.
 9. (canceled)
 10. (canceled)
 11. (canceled)
 12. Acomputer-readable medium having a program of instructions for executionby a computer to perform an electromagnetic wave measurement processusing an electromagnetic wave measurement device including: anelectromagnetic wave output device that outputs an electromagnetic wavehaving a frequency equal to or more than 0.01 [THz] and equal to or lessthan 100 [THz] toward a device under test; an electromagnetic wavedetector that detects the electromagnetic wave which has transmittedthrough the device under test; and a relative position changing unitthat changes a relative position of an intersection across which anoptical path of the electromagnetic wave transmitting through the deviceunder test and the device under test intersect with respect to thedevice under test; said electromagnetic wave measurement processcomprising: deriving a characteristic value of the electromagnetic wavebased on a detection result of the electromagnetic wave detector whilethe characteristic value is associated with an assumed relative positionwhich is the relative position if it is assumed that the electromagneticwave is not refracted by the device under test; changing the assumedrelative position to an actual relative position, which is the relativeposition if the refraction of the electromagnetic wave by the deviceunder test is considered, thereby associating the result derived by thederiving of the with the actual relative position; and deriving thecharacteristic value associated with a predetermined relative positionbased on a result from the changing of the assumed relative position toan actual position.
 13. A computer-readable medium having a program ofinstructions for execution by a computer to perform an electromagneticwave measurement process using an electromagnetic wave measurementdevice including: an electromagnetic wave output device that outputs anelectromagnetic wave having a frequency equal to or more than 0.01 [THz]and equal to or less than 100 [THz] toward a device under test; anelectromagnetic wave detector that detects the electromagnetic wavewhich has transmitted through the device under test; and a relativeposition changing unit that changes a relative position of anintersection across which an optical path of the electromagnetic wavetransmitting through the device under test and the device under testintersect with respect to the device under test so that the intersectionis at a predetermined relative position considering the refraction ofthe electromagnetic wave by the device under test; said electromagneticwave measurement process comprising: deriving a characteristic value ofthe electromagnetic wave based on a detection result of theelectromagnetic wave detector while the characteristic value isassociated with the predetermined relative position.
 14. Acomputer-readable medium having a program of instructions for executionby a computer to perform an electromagnetic wave measurement processusing an electromagnetic wave measurement device including: anelectromagnetic wave output device that outputs an electromagnetic wavehaving a frequency equal to or more than 0.01 [THz] and equal to or lessthan 100 [THz] toward a device under test; an electromagnetic wavedetector that detects the electromagnetic wave which has transmittedthrough the device under test; and a relative position changing unitthat changes a relative position of an intersection across which anoptical path of the electromagnetic wave transmitting through the deviceunder test and the device under test intersect with respect to thedevice under test; said electromagnetic wave measurement processcomprising: deriving a characteristic value of the electromagnetic wavebased on a detection result of the electromagnetic wave detector whilethe characteristic value is associated with an assumed relative positionwhich is the relative position if it is assumed that the electromagneticwave is not refracted by the device under test; and while the relativeposition if a refraction of the electromagnetic wave by the device undertest is considered is an actual relative position, acquiring thecharacteristic value associated with the assumed relative positioncorresponding to the actual relative position closest to a predeterminedrelative position from the result of deriving a characteristic value ofthe electromagnetic wave, and associating the acquired characteristicvalue with the predetermined relative position.
 15. The electromagneticwave measurement device according to claim 2, wherein the characteristicvalue is any one of an attenuation ratio, a group delay, and a chromaticdispersion of the electromagnetic wave.
 16. The electromagnetic wavemeasurement device according to claim 2, wherein the relative positionis represented by an angle between the intersection and a predeterminedaxis, and a coordinate of an orthogonal axis orthogonal to thepredetermined axis at an intersection point between the orthogonal axisand the intersection.
 17. The electromagnetic wave measurement deviceaccording to claim 3, wherein the characteristic value is any one of anattenuation ratio, a group delay, and a chromatic dispersion of theelectromagnetic wave.
 18. The electromagnetic wave measurement deviceaccording to claim 3, wherein the relative position is represented by anangle between the intersection and a predetermined axis, and acoordinate of an orthogonal axis orthogonal to the predetermined axis atan intersection point between the orthogonal axis and the intersection.